Method of carbonizing animal fiber materials



m. BQQ QAQS 1 Jan. 10, 1967 E. SPERK ETAL 3,297,405

METHOD OF CARBONIZING ANIMAL FIBER MATERIALS A I I Filed N02. 23, 1964 3Sheets-Shae; l

WOOL FELT WOOL FELT WOOL FABRIc WOOL FABRIC wooI. FIBER WOOL FIBERIIvIIvIERs. IN HEATING To WASTE 5 CH 0 'c AT AIR 25O%O/HOUR SOLUT ONDRYING IN AIR HEATING o WASTE GAS HEATING TO WASTE GAS ,2ooc 300C AT ,AT5-50/HOUR I IM ITE0 I-Io/HouR AI INGRESS +NH 0R co 0R I CHZO 0R CO2+NH3L|M|TED HEATING TO WASTE GAS AIR ,3ooc AT HEATING To IO-IOO/ HouR iHEATING TO I IOOOC AT OPTIONAL l0|OO/HOUR T I 0PTIoNAI I V YGRAPHITIZING sRAPHITIzINs UP To 3oooc UP To 3oooc Fig. l Fig.2

E. SPERK ET AL METHOD OF CARBONIZING ANIMAL FIBER MATERIALS Filed Nov.23, 1964 WOOL FELT WOOL FABRIC WOOL IBER H EATING TO 200C AT 5-500 HOURLIMITED AIR INGRESS HEATING TO 300C AT l-IO/ HOUR 3 Sheets-Sheet 2"WASTE GAS WASTE GAS +AMMONIUM SALTS L OPTIONAL GRAPHITIZING UP TO 3000CJan. 10, 1967 SPERK ETAL 3,297,405

METHOD OF CARBON IZING ANIMAL FIBER MATERIALS Filed Nov, 23. 1964 .5Sheets-Sheet 3 F'gi. 7b 6b zcamwuc TAPE OF CONDUCTING WEB MATERIALGRAPHITE SINSULATYVION OF CARBON FELT United States Patent Ofifice3,297,405 Patented Jan. 10, 1967 3,297,405 METHOD OF CARBONIZING ANIMALFIBER MATERIALS Edgar Sperk, Meitingen, near Augsburg, Otto Vohler,Nordendorf, near Meitingen, and Franz Jeitner and Volker Gierth,Meitingen, near Augsburg, all of Germany, assignors toSiemens-Planiawerke Aktiengesellschaft fiir Kohlefabrikate, Meitingen,near Augsburg, Germany, a corporation of Germany Filed Nov. 23, 1964,Ser. No.-4I3,679 Claims priority, application Germany, Nov. 21, 1963,

15 Claims. (Cl. 23209.1)

Our invention relates to a method of carbonizing or partiallycarbonizing a wool-containing material, the

term \vool being herein used to designate sheep wool as well as otherfibrous substance of animal origin.

It is known to carbonize or graphitize a fiber-containing material whosefibrous constituents consist of cellulose or regenerated cellulose.

If an attempt were made to subject wool-containing material to heattreatment similar to those known for carbonizing fibrous cellulosematerials, various difficulties would be encountered. The woolcontainingshare of the material would become deformed at the ele vatedtemperatures and thus lose its original fibrous structure. whyheretofore thecarbonizing process has been limited to cellulosematerials.

Itis an object of our invention to provide a method of producing acarbonized, partially carbonized or fully graphitized product from astarting material which contains wool or other animal fiber, and topreserve in the resulting carbonized product essentially thev cohesion,elasticity or pliability of the starting material.

Referring to web or felt material of animal fiber, particularly woolfelt, to be used as starting material, it is another more specificobject of the invention to afi'ord producing a felt-like web structureof carbon which still remains well bendable without breaking and whichcan be fabricated with substantially the same case as the starting webmaterial but, due to carbonization, is applicable as a carbon orgraphite product, for example as an electrical and thermal insulatingmaterial at high temperatures such as up to 3000 C. or more.

To achieve these results, and in accordance with our invention, wesubject the animal-fiber containing material to a carbonizing heattreatment at a temperature up to about l000 C. in tl1cat least temporarypresence of fiber-structure preserving substance. We have found that thepresence of air in the carbonizing furnace has this effect if it is keptin motion or circulation within the furnace, and no fresh air is added.According to another feature of the invention, a fiber preservingsubstance such as formaldehyde, ammonia. carbon dioxide or mixturesthereof may be applied to the wool-containing material during thecarbonizing process. 7

According to'another feature of the invention, we carbonize thewool-containing material in continuously consecutive temperature stagesof respectively different rates of temperature change and progressivelyreduced air supply, the last stage up to about 1000 C. being carried outunder exclusion of air. Preferably, this graduated process is performedin air up to about 200 C. with a temperature increase of to 50 C. perhour, then up to about 300 C. with a reduced air supply at a rate of lto 10 C. per hour, and thereafter concluded up to about 1000 C. underair exclusion at a rate of 10 to 100 C. per hour.

It has been found that in material carbonized according to theinvention, the sulphur links or bridges in the wool fibers are largely,or to an essential extent, preserved.

' C., or even up to 3000 C. In this case, too, the material produced bythe ultimate graphitizing from the wool-con- This seems to have been oneof the reasons taining starting material is still well bendable and thuscan be readily brought into the particular shape required for a heatingconductor or for other purposes.

Products. made according to the invention can also be employed for allother purposes of carbon and graphite materials. In addition, since suchproducts'are flexible or bendable, the field of application, heretoforeoften limited by lack of flexibility or pliability, is considerablywidened. v

For further explanation. reference will be made to specific examplesdescribed hereinafter, as well as to the accompanying drawing in which:

FIGS. 1, 2 and 3 are respective flow sheets relating to differentembodiments of the process according to the invention; and

FIG.'4 shows in section a vacuum furnace equipped with a heater and withinsulating structure, both consisting of material produced according tothe invention.

Example 1 A piece of a soft, 8 mm. thick wool felt of about 500 x 600mm., spread fiat, is placed into a dryer cabinet having a ventingoutlet. The dryer cabinet is first heated up to 240 C., the increase intemperature being about 10 C. per hour. Thereafter the cabinet isfurther heated up to 300 C. but at a slower rate, namely at atemperature increase of 5 C. per hour. During heating of the cabinetfrom 240 C. to 300 C. and in intervals of about three hours, an amountof 500 g. ammonium carbonate is each time placed into the cabinetbeneath the piece of wool felt. Under the efiect of heat, the ammoniumcompound converts to a gas mixture of ammonia and carbon dioxide havinga partial pressure varying between about 5 and 760 torr (mm/Hg). Thesmoke gases evolving during the thermal treatment of the wool felt arecontinuously exhausted through the venting outlet.

After the temperature of 300 C. is reached, the already partiallycarbonized wool felt is taken out of the dryer cabinet, embedded incarbon powder (soot or aquadag) within a graphite casing, andthcn heatedin a shaft furnace up to about 1000 C. At first the temperature isincreased only slowly. Commencing with 300 C. the

temperature increase is about 4 C. per hour, from 600 C. the temperatureis raised about 10C. per hour, and from 900 C. about 20 C. per hour.After complete coking, the furnace and its contents are permitted tocool, the graphite casing with the material is removed, and the materialis cleaned of the adhering embedding material.

ln tests made in this manner, the specimen was found to have shrunk toabout 470 x 360 mm. However, the originalfiber structure was clearlyrecognizable. The elasticity was preserved to such an extent that thespecimen could be wound upon a round rod of about 20 mm. diameter. Theelectrical resistance value, measured perpendicularly to the surface ofthe specimen, was 8 to 11-10 ohm mm. /m.; measured in the direction ofthe web, the resistance was 5 to 1010, ohm mmF/m. The coetficient ofthermal conductance was lower than 10- kcaL/m. hour C.

= example.

Example 2 50 g. raw shorn (virgin) wool are kept for three hours at 85C. in an aqueous solution of 6% formaldehyde and 2% sodium bisulfite andthen well washed and dried at room temperature. The wool thus treated isplaced into a tubular furnace and heated at a temperature increasing 15C. per hour up to 200 C. During heating, a current of air is suckedthrough the wool at a rate of about 21 liters per minute. Thereafter theincrease in temperature is reduced to 3 C. per hour and the air How to0.1 liter per minute. After reaching a temperature of 300 C., the woolis taken out of the furnace and further processed as described inExample 1.

The carbonized ultimate product obtained by this process exhibited thefiber structure of the original virgin wool. The elasticity orpliability of the starting material was largely preserved. For examplethe carbonized product could be twisted to threads of yarn.

Another specimen of shorn wool treated for 48 hours at 50 C. in anaqueous solution of 6% formaldehyde and 10% sodium hydrosulfite andthereafter processed in the manner described above, exhibited the sameresults with respect to mechanical properties.

Example 3 A specimen web of 100 x 500 mm. size woven from wool cardedyarn and consisting of 80% of pure shorn sheep wool, was placed upon atunnel-shaped insert into a dryer cabinet and then heated atatemperature increasing 20 C. per hour up to 200 C., then at the rate of7 C. per hour up to 300 C. During this heat treatment. when thetemperature of 240 C. was reached, ammonia gas was introduced into thedryer cabinet at a partial pressure between 50 and 200 torr. The ammoniagas atmosphere was maintained until the temperature of 300 C. wasreached.

The further processing corresponded to the one described in Example 1.The ultimate exhibited good tear strength and was elastic. Its square"resistance, that is the resistance value of a square of any edge length,was ohm.

During a subsequently performed graphitizing process up to 2700 C.,thissquare resistance was reduced to 1 ohm.

Graphitized material thus produced is particularly well applicable as aheating conductor, preferably in tape form, as well as for various otherpurposes.

The sulphur content of the latter specimen was analized prior to, andafter, the thermal treatment. It was found that the sulphur content ofthe starting material was 3.03% by weight and had declined to 2.28%after the thermal treatment. This slight reduction in sulphur content isstill negligible as regards preservation of elasticity or pliability ofthe ultimate material.

Further modes of performing the process of the invention will bedescribed with reference to the drawings.

According to the process represented by the fiow sheet in FIG. 1 thestarting material (for example wool felt, wool fabric or raw animalwool) is immersed in an aqueous solution of formaldehyde in the presenceof a reduction agent, such as sodium bisulfite, and thereafter dried inair. Thereafter the material is heated with access of air to atemperature of 200 C. at a rate of 5 to 50 C./hour, and the evolvingvapors and gases are continuously withdrawn. Thereafter the material isfurther heated with a reduced ingress of air, up to 300 C. at a rate of1 to 10 C./hour, the evolving waste gases being likewise withdrawncontinuously. The further heating up to 1000". C. is applied at-a rateof 10 to 100 C./hour under exclusion of air.

According to the process represented diagrammatically in FIG. 2, thestarting material is first heated up to 3000 4 C. in the mannerdescribed above with reference to FIG. 1. However, during the processingperiod between 200 and 300 C. a substance or mixture, such asformaldehyde, ammonia and/or carbon dioxide, in gaseous constitution issupplied, resulting in a partial pressure of these gases between about 5and 760 torr. The subsequent heating up to 100 C. corresponds to theprocessing stage described above with reference to FIG. 1.

According to the process represented in FIG. 3, the thermal treatment iscarried out in the same manner as described in the foregoing, exceptthat an ammonia compound or a mixture of ammonium compounds is directlyadded during the heating period between 200 and 300 C. for the purposeof supplying ammonia and, as the case may be, also carbon dioxide.

The material resulting from the processes exemplified by FIGS. 1, 2 and3 may be additionally subjected to graphitizing under exclusion of airin the known manner at temperatures up to 3000 C. p

The vacuum furnace illustrated in FIG. 4 represents an example in whichanimal fiber material processed according to the invention-is employedfor two different purposes. The furnace comprises a vacuum-tight jacket1 of sheet metal which surrounds a cylindrical heater body composed of aceramic carrier tube 2 and a helical conductor tape'3 mounted on theouter cylindrical surface of the ceramic tube 2. The conductor tape 3consists of a fabric processed according to the invention andgraphitized at temperatures up to about 2700 C. The fiber structure andthe pliability of the fibrous material are preserved in the tape so thatit could be wound about the ceramic tube 2. The resistance value of thetape 3 was reduced during the graphitizing process to such an extentthat the graphitized material became suitable and advantageous for useas a heating resistor. Shoved over the heater body 2, 3 is a cylindricaltube 4 of graphite which is heat insulated by a surrounding material 5constituted by several concentric layers. This insulating material 5consists of carbonized wool felt made by a method according to theinvention.

The ceramic tube is closed at both ends by respective ring-shaped coverplates 60 and 6/). The end of a cy lindrical duct 7a, 7b is joined witheach ring-shaped cover plate, The other end of each duct passes throughthe wall of the vacuum-tight jacket 1 and is heat-insulated therefrom byan insulating sealing member of annular shape.

The cylindrical conduits 7a and 7b thus form a connection between theinterior of the ceramic tube 2 and the vicinity of the furnace and maybe used for supplying and removing of the material to be heated in thefurnace.

A free space remains between the vacuum-tight jacket 1 and the heaterbody of the furnace. During operation of the furnace the heat transferthrough this interspace can be reduced. by evacuating it through anipple 8 of jacket 1.

We claim:

1. The process of carbonizing animal fiber material, which comprisessubjecting the ainmal fiber material to carbonizing heat treatment inseveral consecutive stages of gradually increasing temperature up toabout 1000 C., permitting access of air to the material during the firststage, and reducing such access during the subsequent stages down toexclusion of air in the last stage, whereby the resulting carbonizedmaterial substantially retains mechanical fiber characteristics of thestarting material.

2. The process of carbonizing animal fiber material,

which comprises heating the animal fiber material in air up to about 200C. at a rate of 5 to 50 C. per hour, then further heating the materialwith a limited air supply up to about 300 C. at a rate of 1 to 10 C. perhour, and thereafter continuing the heating of the material underexclusion of air up to about 1000 C. ata rate of 10 to C, per hour.

3. The process of carbonizing animal fiber material, which comprisesheating the animal fiber material at a gradually increasing temperatureup to about 1000" C., and applying to the material during theheatingperiod with proteinaceous fiber preserving substance. v

4. The process of carbonizing animal fiber material, which comprisesheating the animal fiber material at a gradually increasing temperatureup to about 1000" C., and applying to the material during the heatingperiod at least one substance from the group consisting of formaldehyde,ammonia, carbon dioxide and mixtures thereof,

whereby the resulting carbonized material substantially retainsmechanical fiber characteristics of the starting material.

5. The process of'carbonizing animal fiber material, which comprisessubjecting the animal -fiber material to carbonizing heat treatment inseveral consecutive stages of gradually increasing temperature up toabout 1000 C., permitting access of air to the material during the firststage, reducing such access during the subsequent stages down toexclusion of air in the last-stage, and applying to the material duringthe heat treatment at least one substance from the group consisting offormaldehyde, ammonia, carbon dioxide and mixtures thereof.

a 6. The process, according to claim 2, which comprises applying to thematerial during heating at a temperature above 200 C. at least onegaseous substance from the group consisting of formaldehyde, ammonia,carbon dioxide and mixtures thereof.

7. The process according to claim 6, which comprises adding saidsubstance at a temperature between about 240 C. and about 300 C. at apartial pressure of 5 to 760 torr.

S. The process according to claim 1, which comprises adding to theanimal fiber material an ammonium compound, whereby said heat treatmentcauses said compound to evolve gaseous ammonia.

9. The process of carbonizing animal fiber material, which comprisesimpregnating the animal fiber material with formaldehyde, thensubjecting the impregnated material to carbonizing heat treatment inseveral consecutive stages of gradually increasing temperature up toabout 1000 C., permitting access of'air to the material during the firststage, and reducing such access during the subsequent stages down toexclusion of air in the last stage.

10. The process of carbonizing animal fiber material, which comprisesimmersing the animal fiber material in an aqueous solution offormaldehyde, drying the material, then subjecting the dried material tocarbonizing heat treatment in several consecutive stages of graduallyincreasing temperature up to about 1000 C., permitting access of air tothe material duringthe first stage, and reducing such access during thesubsequent'stages down to exclusion of air in the last stage.

11. The process according to claim 10, wherein said aqueous solution offormaldehyde contains an addition of bisulfite reaction agent. i

12. The process according to claim 10, wherein said aqueous solution offormaldehyde contains an addition of sodium bisulfite.

13, The process according to claim 1, which comprises exhausting, up toa temperature at least of about 300 C., the vapors and gases evolvingfrom the material being carbonized.

14. The process of carbonizing animal fiber material, which comprisessubjecting the animal fiber material to carbonizing heat treatment inseveral consecutive stages of gradually increasing temperature up toabout 1000" C.,

permitting access of air to the material during the first stage,reducing such access during the subsequent stages down to exclusion ofair in the last stage, and thereafter graphitizing the material underexclusion of air at ternperatures above 1000 C. up to about 3000" C.

15. The process of carbonizing animal fiber material, which comprisesheating the animal fiber material at a gradually increasing temperatureup to about 1000 C., applying to the material during the heating periodat least one substance from the group consisting of formaldehyde,

ammonia, carbon dioxide and mixtures thereof, and thereaftergraphitizing the material under exclusion of air at temperatures above1000 C., up to about 3000 C.

References Cited by the Examiner UNITED STATES PATENTS NORMAN G.TORCHIN, Primary Examiner.

J. CANNON, Assistant Examiner.

1. THE PROCESS OF CARBONIZING ANIMAL FIBER MATERIAL, WHICH COMPRISESSUBJECTING THE ANIMAL FIBER MATERIAL TO CARBONIZING HEAT TREATMENT INSEVERAL CONSECUTIVE STAGES OF GRADUALLY INCREASING TEMPERATURE UP TOABOUT 1000* C., PERMITTING ACCESS OF AIR TO THE MATERIAL DURING THEFIRST STAGE, AND REDUCING SUCH ACCESS DURING THE SUBSEQUENT STAGES DOWNTO EXCLUSION OF AIR IN THE LAST STAGE, WHEREBY THE RESULTING CARBONIZEDMATERIAL SUBSTANTIALLY RETAINS MECHANICAL FIBER CHARACTERISTICS OF THESTARTING MATERIAL.
 14. THE PROCESS OF CARBONIZING ANIMAL FIBER MATERIAL,WHICH COMPRISES SUBJECTING THE ANIMAL FIBER MATERIAL TO CARBONIZING HEATTREATMENT IN SEVERAL CONSECUTIVE STAGES OF GRADUALLY INCREASINGTEMPERATURE UP TO ABOUT 1000*C., PERMITTING ACCESS OF AIR TO THEMATERIAL DURING THE FIRST STAGE, REDUCING SUCH ACCESS DURING THESUBSEQUENT STAGES DOWN TO EXCLUSION OF AIR IN THE LAST STAGE, ANDTHEREAFTER GRAPHITIZING THE MATERIAL UNDER EXCLUSION OF AIR ATTEMPERATURES ABOVE 1000*C. UP TO ABOUT 3000*C.